In order to disperse sludge and the like in engine oil to maintain cleanliness inside an engine, various lubricating oil additives represented by alkaline earth metal salts have been used. When these additives possess a high basicity, they are very economical due to a lower amount of required additive. However, the stability of these additives declines, resulting in problems such as gelling which forms a film on the surface of the engine and the like. For this reason, fatty acids are added to overcome these problems (for example, refer to Patent Document 1).
In regard to 2-cycle engine oils, since a portion of the engine oil is discharged along with the exhaust gas, engine oil used in outboard motors and so on has been required to possess biodegradability and heat stability.
As a carboxylic acid used as an additive in engine oil, tertiary carboxylic acids such as 3-methyloctane-3-carboxylic acid, secondary carboxylic acids such as 2-ethylhexanoic acid and isostearic acid, and the like can be used, and long-chain branched primary carboxylic acids having 20 or more carbon atoms are not known. These compounds do not fully exhibit the properties of low temperature fluidity, low volatility, biodegradability, and the like required for lubricating oil additives.
Various carboxylates are known to be used in the base stock of lubricating oils. For example, mineral oils are used in lubricating oils for chainsaws used in lumber logging. However, in recent years, in consideration of environmental problems, the use of biodegradable plant oils such as rapeseed oil (triglyceride of fatty acid) has been proposed (for example, refer to Patent Document 2).
Although these plant oils are biodegradable, they are unstable and possess poor low temperature properties due to unsaturated bonds contained therein, which limits their use as lubricating oils.
In order to improve thermal stability, the use of synthetic ester has been disclosed (for example, refer to Patent Document 3). However, good low temperature properties cannot be obtained.
An ester-type lubricating oil with improved flow characteristics at room temperature while ensuring biodegradability has been disclosed (for example, refer to Patent Document 4). However, since the carboxylic acid used possesses a comparatively short chain of up to 10 carbon atoms, the lubricating oil does not possess a satisfactory viscosity index, which is an important indicator of lubricating oil characteristics.
Although carboxylic acids used in paint coatings, epoxy resin reformers, plasticizers, cosmetic base materials, raw materials for stabilizers, and the like have been desired to be in a liquid state and possess a high boiling point in view of handling easiness, a compound satisfying these characteristics has not been known.    [Patent Document 1] JP-A-1988-203645    [Patent Document 2] JP-A-1993-230490    [Patent Document 3] JP-A-1993-98276    [Patent Document 4] JP-A-2000-514470